When he was first introduced, Rantaro seemed like a mysterious individual. Later it could be seen that he is a carefree and relaxed person, and he is actually described as one of the more ordinary students despite his mysteriousness, with he himself stating that he can sometimes get a bit overwhelmed by the others' stranger personalities. Nevertheless, he is shown to have more patience with some eccentric students like Kokichi and Miu, with a tendency to just laugh off some of things they say. Even though Rantaro cannot remember his talent, he doesn't seem worried about it, instead, he simply looks forward to finding out what it is. He is usually seen smiling and describes himself as "not a suspicious guy". He gives off a really calm and composed vibe and seems like a reliable person.

Despite his appearance and manner of speech, he has cold, excellent insight, and he is both determined and brave. He even has downright frightening expressions whenever he gets very serious.